Even though Jon Krakauer was surrounded by death on Everest, he still finds peace at high altitudes. On this day, seven years after his tragic expedition became the basis for ”Into Thin Air” (which has sold over 3.6 million copies), the 49-year-old author chooses a mountain trail high above Boulder, Colo., as the backdrop to discuss ”Under the Banner of Heaven,” his first book since he became both a best-selling author and an odd sort of celebrity. In the distance, reaching into the clouds, is a monolithic row of vertical sandstone shards called the Flatirons. Krakauer says he climbs them when he needs to escape.

He may need to do a lot of climbing soon. After all, his new book is creating an avalanche of controversy. Banner is both an expose on Mormon fundamentalists – a growing fringe group who still practice polygamy – and the true-crime story of Dan and Ron Lafferty, Mormon fundamentalist brothers who murdered a young woman and her daughter on July 24, 1984. They claim that God ordered them to do it.

EW Did you stop climbing after Everest?JON KRAKAUER I didn’t really. After Everest, I got invited on this climb in Antarctica. I thought twice about it, but it was with six friends – none of the client-guide weirdness. It reminded me what was good about climbing. There’s risk involved, but the rewards are worth it, I think. I mean, you can’t make that argument to someone who’s lost a husband or a son, but…

EW What are those rewards?JK It sounds hokey, but there’s a spiritual component. I grew up in a family of atheists, so the closest I’ve ever had to religion is climbing. You spend all night hanging off the side of a cliff in a bivouac in a blizzard, and then the sun comes up and you’re still alive – that’s sort of profound.

EW Do you see a theme between ”Into the Wild” [his 1996 best-seller about a young loner who roams the woods of Alaska], ”Into Thin Air,” and the new book?JK It was pointed out to me by my publisher looking for a way to market the book. ”How are we going to market this to people who are looking for the next ‘Into Thin Air’?” I guess I’m drawn to people who become obsessed with these quests.

EW This wasn’t the book you started out to write, though, was it?JK The book originated as an attempt to examine the nature of religious belief. I was driving across southern Utah and I stopped for gas in Colorado City [Ariz.]. And there were all of these people in weird clothes and these little girls dressed in their 19th-century garb on a 140-degree day. It was a polygamous community. And I was like, ”Whoa, why haven’t I heard of this?! Ten thousand polygamists!” The true-crime aspect, the Lafferty story, just became the narrative engine…a means of exploring why and how people do these incredibly nasty things in the name of God.

EW What do you think the reaction will be from the Mormon Church?JK They’ve already basically let it be known that good Mormons should not read this book. And I think they will be very uncomfortable with the history; they will not like the fact that I point out that Joseph Smith told 14-year-old girls ”God says you should marry me, if you don’t…” His way of getting laid doesn’t reflect well on him.